Fuse plug



March 18, 1930. G. R. BROWN 1,751,439

FUSE PLUG Filed Feb. 28, 1928 Fig].

lrn/entor I G60) 6 R. Brown, Joywfl l/w Hi8 Attorn ey.

Patented Mar. 18, 1930 UNITED STATES PATENT OFFICE GEORGE R. BROWN, OF BRIDGEPORT, CONNECTICUT, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK FUSE PLUG Application filed February 28, 1928. Serial No. 257,704.

The present invention relates to thermal cut-outs for the protection of electric circuits from unsafe flow of current and more especially to plug fuses.

The object of my invention is the provision of an improved fuse plug which shall be highly efficient in interrupting an excess flow of current, of small overall dimensions, substantially indestructible and of low manufacturing cost.

One embodiment of the invention is shown in the accompanying drawing in which Fig. 1 is a vertical section of the plug at an enlar'ged scale; Fig. 2 is a perspective view of the constituent parts of the plug separated from each other, and Fig. 3 is an underside plan view of the outer shell.

As shown in the drawing, the plug has a cup-shaped base 1 of porcelain or other insulating material with a cylindrical projection 2 at the lower end of substantially less diameter than the main outer wall 3 of the base and having a central bore 4 extending therethrough with a countersunk recess 5 at the lower end for the .reception of a metal center contact 6 in the form of a beaded eyelet, the c lindrical portion 7 of which extends through the bore 4 and its upper end is flanged over the upper corner of said bore. The countersunk recess 5 is made sufficiently deep to permit the center contact completely to enter above the lower end of the cylindrical projection 2 so that the latter forms a protective wall 8 about and below the contact. The radial shoulder 9 of the base 1 outside the cylindrical projection 2 is provided with a number of rectangular lugs 10 and the main outer wall 3 has a notch 11 formed in its upper edge.

The fusible link 12 consists of a strip of flat soft metal with a centrally reduced portion 13. One end of the link is secured to the center contact 6 by means of soft metal slugs 4 deformed within the cylindrical portion 7 after insertion of the end of the link therein. The link extends outwardly through the chamber of the cup-shaped base, passes through the notch 11 and is bent down past the outer wall thereof.

The outer shell comprises a screw shell contact 15 in the form of a metal cylinder with a screw thread 16 impressed in its lower portion, while the upper portion is plain with its upper edge 18 bent inwardly and a hand hold shell 19 of insulating material, such as bakelite, moulded about the upper portion of the screw shell contact 15 so as to imbed the upper edge 18 therein. A sight aperture 20 is formed in the end wall of the hand hold shell 19 and the inner radial wall 21 thereof is provided with a maze of gas vent passages or grooves 22 with outlets 23 opening into the sight aperture 20, as indicated in Fig. 3.

A transparent disk 24, such as mica, of a diameter slightly less than the internal diameter of the screw shell contact 15 serves to complete the outer shell and forms a window therein through which the condition of the fuse link 12 may be inspected. When the outer shell is in assembled relation to the base 1 the disk 24 rests on the top of the cylindrical wall 3 of the base and closes the chamber thereof.

An internally flanged metal holding ring 25 of a diameter to fit within the screw contact 15 has notches 26 cut in its flange to receive and interlock with the lugs 10 on the base 1 and upon being inserted within the screw shell contact with the outer end of the fuse link 12 disposed between the inner surface of the screw shell contact 16 and the outor surface of the holding sleeve 25, the several parts are permanently united by joining the lower edges thereof as by means of solder 27. The ring 25, by its positive connection to the outer shell and through its engagement with the shoulder 9 and lugs 10 of the base, serves to hold the parts in fixed relation axially and rotatably. It also reinforces the threaded end of the screw shell and leaves a substantial annular space about the cylindrical base projection 2. In case it is desired to depend upon other means than solder for holding the parts of the plug assembled, the outer shell is locked against relative rotation to the base by a teat 28 formed on the inner cylindrical wall of the former which enters and engages the sides of the notch 11 in the upper edge of the base Wall 3.

Upon the occurrence of an excess current in a. circuit protected by the plug, the fusible link blows or fuses giving 05 a considerable volume of hot gas which expands in the plug chamber and escapes gradually therefrom by passing about the periphery of the mica disk 24, into and through the maze of passage ways 22 and escapes'throughthe outlets 23. Initstravel through the vent passages a large amount of the heat of the gas is conducted away so that when it finally escapes it is incapable of igniting easily combustible material, and on account of the direction of the gases it finally escapes being toward the center of the plug, there is no danger of its scorching or blackening the hand of a person in case of blowing during installation.

While my fuse plug is especially designed for use with receptacles having their screw shells protected by an insulating inner shell, as in my prior application, Serial No. 216,003, filed Au st 29, 1927, it may be used to advantage witli any of the other forms of receptacles now in general use.

While I have shown and described the best form of the invention known to me, I do not desire to be restricted thereto.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A fuse plug comprising a peripherally shouldered insulating base having a chamber open at the top thereof and a center contact in the bottom end thereof, an outer shell surroundin the top and sides of said base and provided with a screw-threaded contact, a

holding ring mounted within and secured to said screw-threaded contact and engagin the peripheral shoulder of said base, and a usible link extending through said chamber and connected at its ends with said center and screw-threaded contacts respectively.

2. A fuse plu comprising a cup-shaped insulating base aving a cylindrical projection and a radial shoulder at the lower end, a center contact mounted in said cylindrical projection, an outer shell comprising an in sulating hand hold and a screw-threaded congact surrounding the too and sides of said ase, threaded contact and provided with an inturned flange at its upper end to engage the radial shoulder of said base, and a fusible link connected at'its ends with said centerand screw-threaded contacts respectively.

3. A fuse plug comprising a cup-shaped base having on its lower end a central projection and a radial shoulder with spaced lugs thereon. a center contact mounted in said projection, an outer shell comprising an insulating hand hold and a screw-threaded contact surrounding the top and sides of said base, a holding ring secured within said screw-threaded contact and provided at its upper edge with an inturned and notched flange to engage said radial shoulder and lugs of the base, and a fusible link connected at its a holding ring secured to said screwends to said center and screw-threaded contacts res ectively.

4' A use plug comprising a base with a fuse chamber at the upper end thereof, a center contact mounted in the lower end of said base, an outer shell enclosing the upper end and sides of said base and comprising a screw-threaded contact and an insulating hand hold moulded upon the screw-threaded contact and provided in its inner end wall with a grooved maze and an insulating disk, a holding ring mounted within said screwthreaded contact and engaging said base, and a fusible link connecting said center and screw-threaded contacts.

In witness whereof I have hereunto set my hand this 21st day of Februar 1928.

GEORGE BROWN. 

